Low energy production of alcohols and gasoline blends with mixed higher alcohols

ABSTRACT

A method of producing a mixed higher alcohol blend is disclosed which may be self contained both composition-wise with regard to the specific alcohols as well as energy-wise. In one embodiment, the energy created during an exothermic Fischer-Tropsch reaction is utilized to drive downstream distillation column reboilers in a cascade mechanism, thereby providing a low energy process. In one embodiment, an extraction process is performed utilizing a suitable solvent and the co-solvent capabilities of the C4+ higher alcohols already present in the aqueous alcohol stream provided to the extraction column.

TECHNICAL FIELD

Embodiments of the present invention relate to the field of producing alcohols and mixed higher alcohol blends.

BACKGROUND

Gasoline-alcohol blends are becoming increasingly attractive as fuels as the price of gasoline increases and the supplies from conventional sources are reduced. For example, the use of gasoline-ethanol blends known as “gasohol” is rapidly expanding in internal combustion engines to reduce the amount of gasoline consumption, increase the octane rating and reduce carbon monoxide emissions.

Alcohols can be derived from a variety of sources such as the fermentation of sugars, starches and cellulose, and can also be prepared synthetically. For example, synthesis gas containing hydrogen (H₂), carbon monoxide (CO), and optionally carbon dioxide (CO₂) can be converted directly to alcohols and water in accordance with a Fischer-Tropsch synthesis. The production of alcohols in such a manner is faced with the issue of separation of the alcohols from each other as well as from co-produced water (dehydration), which can be quite energy intensive and costly.

Dehydration of alcohols can be accomplished utilizing methods such as azeotropic distillation with entraining agents, use of various adsorbents, and extraction. U.S. Pat. No. 2,356,348 illustrates the use of azeotropic distillation of ethanol from water by adding a C₈-C₁₂ hydrocarbon entraining agent to an ethanol-water solution. U.S. Pat. No. 4,447,643 illustrates the use of cyclic and heterocyclic amines to extract ethanol from an ethanol-water solution. In order to integrate either dehydration method into a commercial-grade gasohol composition, the entraining agent and/or extractant must be generally be separated from the ethanol subsequent to dehydration and prior to blending with gasoline thereby adding unwanted materials and processing cost to the process. U.S. Pat. No. 4,490,153 illustrates the use of gasoline to extract the ethanol directly from an ethanol-water solution for gasohol production. However, U.S. Pat. No. 4,490,153 discloses that extraction of the ethanol with gasoline directly from an ethanol-water solution is shown to require a significantly high ethanol concentration of at least 90 wt % in the ethanol-water solution, which requires considerable separation energy in an initial distillation stage prior to extraction of the ethanol with gasoline. Otherwise, the extracted ethanol-gasoline blend has been found to include too much water to be used as a fuel for internal combustion engines.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a method of producing a mixed higher alcohol blend in accordance with an embodiment of the invention.

FIG. 2A is an illustration of a catalyst train in accordance with an embodiment of the invention.

FIG. 2B is an illustration of a separation train in accordance with an embodiment of the invention.

FIG. 3 is an illustration of a thermal integration scheme in accordance with an embodiment of the invention.

FIG. 4 is an illustration of a thermal integration scheme in accordance with an embodiment of the invention.

SUMMARY

In an embodiment, a method of producing a mixed higher alcohol blend is described. An aqueous alcohol stream including mixed lower and higher alcohols is provided. For example, the aqueous alcohol stream may be provided by passing a synthesis gas comprising hydrogen (H₂), carbon monoxide (CO) and carbon dioxide (CO₂) through a catalytic zone favoring the production of C1-C5+ alcohols. The C1-C2 lower alcohols, and optionally iso-propanol, are then removed from the aqueous alcohol stream. This may be accomplished through a distillation technique. The resultant aqueous stream may comprise at least a 1:1 weight ratio of C3 to C4+ alcohols such that the total weight of C4+ alcohols is greater than or equal to the total weight of C3 alcohols in the resultant aqueous alcohol stream. In an embodiment, the resultant aqueous alcohol stream may comprise at least a 1:1.4 wt ratio of C3 to C4+ alcohols. The C3+ higher alcohols are then extracted from the resultant aqueous alcohol stream utilizing a suitable solvent.

In an embodiment, the energy created during an exothermic Fischer-Tropsch reaction is utilized to drive downstream distillation column reboilers in a cascade mechanism, thereby providing a low energy process. The downstream distillation processes may be driven using no more energy than is provided from the Fischer-Tropsch reaction.

DETAILED DESCRIPTION

Embodiments of the present invention disclose methods of producing alcohols and mixed higher alcohol blends. In an embodiment, a low energy method of preparing mixed higher alcohols blended with gasoline is disclosed.

In the following description, numerous specific details are set forth, such as specific configurations, compositions, and processes, etc., in order to provide a thorough understanding of the present invention. In other instances, well-known processes and manufacturing techniques have not been described in particular detail in order to not unnecessarily obscure the present invention. Furthermore, it is to be understood that the various embodiments shown in the Figures are illustrative representations and are not necessarily drawn to scale.

As used herein, the term “higher alcohols” means C3 or higher alcohols (e.g. propanol, butanol, pentanol, hexanol, etc.). Consequently, the term “lower alcohols” means C2 and lower alcohols (e.g. ethanol and methanol). The notation of C3+ includes alcohols having three carbons (e.g. propanol) and alcohols including more than three carbons. Likewise, the notation of C4+ includes alcohols having four carbons (e.g. butanol) and alcohols including more than four carbons.

In some embodiments, methods of producing gasoline blends with mixed higher alcohols are disclosed which may avoid some of the current problems associated with the production of gasohol blends. For example, it may not be necessary to separate an entraining agent and/or extractant subsequent to dehydration and prior to blending with gasoline, which may avoid adding unwanted materials and processing costs to the process. In addition, the extraction of alcohols from an aqueous alcohol solution may not be overly sensitive to the amount of water in the aqueous alcohol solution, and therefore a prohibitive amount of separation energy is not required in the initial distillation stage prior to extraction, thereby allowing for an overall lower energy separation process.

In one aspect, a method of producing a gasoline blend with mixed higher alcohols is disclosed which may be self contained both composition-wise with regard to the specific alcohols as well as energy-wise. As described in more detail with regard to the Figures, in accordance with embodiments of the invention the energy created during an exothermic Fischer-Tropsch reaction may be utilized to drive downstream distillation columns in a cascade mechanism, thereby providing a low energy process. As a result, any downstream distillation processes may be driven using no more energy than is provided from the Fisher-Tropsch reaction. In accordance with additional embodiments of the invention, an extraction process may be performed utilizing a suitable solvent and the co-solvent capabilities of the C4+ higher alcohols already present in the aqueous alcohol stream provided to the extraction column. By selecting the proper catalyst for use in the Fischer-Tropsch reaction, the desired ratio of C3 to C4+ alcohols is produced in the catalyst train process and later utilized in the separation train process to aid in the extraction of C3+ alcohols from water to result in a substantially water free extract. Where the solvent is gasoline, the extract may be suitable for use as a transportation fuel.

FIG. 1 is an illustration of a method of producing a mixed higher alcohol blend in accordance with an embodiment of the invention. As illustrated in FIG. 1, an aqueous alcohol stream including mixed lower and higher alcohols is first provided at operation 110. For example, an aqueous alcohol stream may be provided by passing a synthesis gas comprising hydrogen (H₂), carbon monoxide (CO), and carbon dioxide (CO₂) through a catalytic zone under conditions favoring the synthesis of C1-C5+ alcohols. The effluent can then be cooled and the resulting aqueous phase containing water and C1-C5+ alcohols is separated from the unconverted vapor phase H₂, CO, and CO₂ to obtain an aqueous alcohol stream.

The aqueous alcohol stream may then be provided to a distillation column at operation 120 to remove the lower alcohols, and optionally iso-propanol, from the aqueous alcohol stream, resulting in at least about a 1 to 1 weight ratio of C3 to C4+ alcohols in the resultant aqueous alcohol stream such that the total weight of C4+ alcohols is greater than or equal to the total weight of C3 alcohols in the resultant aqueous alcohol stream. In an embodiment, the resultant aqueous alcohol stream has at least about a 1 to 1.4 weight ratio of C3 to C4+ alcohols. At operation 130, the resultant aqueous alcohol stream is subjected to an extraction operation with an extracting solvent resulting in a C3+ higher alcohol-rich extract and a substantially alcohol-free aqueous raffinate.

In another aspect, embodiments of the invention recognize that complete separation of C3 and lower alcohols from water in an extraction operation can be particularly problematic due to the affinity and solubility of C3 and lower alcohols in water. Therefore C1-C2 alcohols, and optionally iso-propanol, are removed from the aqueous alcohol stream in operation 120. In accordance with embodiments of the present invention, the solvency of C3 alcohol(s) in water may be overcome by utilizing the co-solvency ability of C4+ alcohols for the C3 alcohol(s). In an embodiment the weight ratio of C3 to C4+ alcohols in the aqueous phase leaving the distillation column at operation 120 and entering the extraction column at operation 130 is at least about 1 to 1 such that the total weight of C4+ alcohols is greater than or equal to the total weight of C3 alcohols in the resultant aqueous alcohol stream. In another embodiment, the weight ratio may be at least about 1 to 1.4.

In another aspect, embodiments of the invention disclose a closed co-solvent extraction process in which the C4+ alcohols in the initial aqueous alcohol stream provided in operation 110 act as co-solvents for the C3 alcohol(s) during extraction operation 130. While not intended to be limited by theory, it is believed that the efficiency of extracting the C3 alcohols(s) from the aqueous alcohol stream increases as the weight ratio of C4+ to C3 alcohols increases, which depends upon the initial ratio of C4+ to C3 alcohols provided in the initial aqueous alcohol stream provided in operation 110. Therefore, by controlling the weight ratio of alcohols in the initially provided aqueous alcohol stream at operation 110, followed by removal of the lower alcohols, and optionally iso-propanol, in distillation operation 120, the extraction operation 130 of the C3+ higher alcohols may be performed in which the need for further dehydration is reduced or even eliminated. In an embodiment, at least 95%, or even 99% of the C3 alcohol(s) are drawn into the extract, while less than 5%, or even 1% of the C3 alcohols(s) fall into the substantially alcohol-free aqueous raffinate. In an embodiment, the water content of the extract is less than 2% by weight, or even less than 0.2% by weight, providing an extract in which the need for further dehydration is reduced or even eliminated prior to use as a fuel.

In one embodiment, the extracting solvent in operation 130 is gasoline. In such an embodiment, the C3+ higher alcohol-rich extract may be suitable for use as a fuel, such as an automotive fuel. It is believed that controlling the ratios of C3 to C4+ alcohols is particularly beneficial when the extracting solvent is gasoline because the particular composition may help prevent phase separation behavior, thereby resulting in a gasoline-alcohol mixture that is resistant to loss of alcohol in the presence of water. In an embodiment, at least 95%, or even 99% of the C3 alcohol(s) are drawn into the extract, while less than 5%, or even 1% of the C3 alcohols(s) fall into the substantially alcohol-free aqueous raffinate, and water content of the extract is less than 2% by weight, or even less than 0.2% by weight.

The distillation of the lower alcohols, and optionally iso-propanol, over the top at operation 120 has several advantages in the resultant fuel compared to some conventional alcohol-gasoline blends which include lower alcohols. For example, methanol is a volatile and toxic chemical, has a phase separation tendency when water is present, and can be further troublesome in gasoline blends leading to difficulty when starting an engine in cold weather. There are also considerable drawbacks with the use of ethanol in gasoline blends. Ethanol has a tendency to erode certain polymer components present in plastic piping, gaskets, and seals. As a result, ethanol-gasoline blends cannot be transferred through pipelines, and therefore must be transported by truck or railway.

In another embodiment, the extracting solvent in operation 130 is an organic liquid such as decane or a non-polar oxygenate such as octyl ether, which is largely immiscible with water, has a partition coefficient with respect to butanol and water greater than one, and a vapor pressure low enough to allow the separation of the extracting solvent via simple distillation. After the extracting operation 130, the product may contain the solvent plus the C3+ alcohols. The product can optionally be dried utilizing, for example, a molecular sieve drying operation, and the alcohols subsequently separated by simple distillation.

In an embodiment, the aqueous alcohol stream in operation 110 is provided by passing a synthesis gas through catalytic conditions to produce a mixture of alcohols in accordance with an exothermic Fischer-Tropsch reaction. The conversion of synthesis gas to alcohols can be carried out utilizing the exothermic Fischer-Tropsch reaction:

2nH₂+nCO→C_(n)H_(2n+2)O+(n−1)H₂O

3nH₂+nCO₂→C_(n)H_(2n+2)O+(2n−1)H₂O

A number of catalysts are available to drive the above reactions such as, but not limited to, copper-cobalt and precious metal catalysts. In an embodiment, copper-cobalt catalysts similar to those described in Sugier, A., et al., “The I.F.P. Way to Produce C1-C5 Alcohols for Use as a Gasoline Blending Component,” International Symposium on Alcohol Fuels Technology, Guaraja, Brazil, October 508, 1980, which is incorporated herein by reference, may be utilized to produce an aqueous alcohol stream including mixed lower and higher alcohols. For example, a copper-cobalt catalyst may be associated to one or more other metals (e.g. Cr, Al, Mn, Fe) or their oxides and alkalized (Li, Na, K, Cs, Fr) or alkalinized (Be, Mg, Ca, Sr, Ba, Ra). The copper-cobalt catalysts may also contain zinc or rare earths (lanthanide series, actinide series, scandium and yttrium).

In an embodiment, a Cr_(0.15)La_(0.15)Al_(0.15)Cu₁Co_(0.5)Na_(0.3) catalyst (in molar proportions) similar to the one disclosed in U.S. Pat. No. 4,346,179, which is incorporated herein by reference, is utilized to produce an aqueous alcohol stream including mixed lower and higher alcohols. By way of example, the catalyst may be prepared from an aqueous solution containing suitable proportions of chromium nitrate, lanthanum nitrate, copper nitrate, cobalt nitrate, a 1N nitrate solution in which is suspended the suitable amount of an alumina having a specific surface of 200 m²/g and a grain size of 10 to 100 microns. Under strong stirring a precipitate is formed by a 0.5 N solution of sodium carbonate. The precipitate is washed several times and dried at 500 ° C. for 24 hours; this precipitate is then impregnated with a solution of sodium acetate whose concentration has been so adjusted as to obtain the desired sodium content of the catalyst. After drying for 6 hours at 120° C., the product is treated for 6 hours at 400° C. in air; the resulting powder is pelletized to pellets of a 5 mm diameter and a 5 mm height.

In another embodiment, a Cu₁Co₁Cr_(0.8)K_(0.09) catalyst (in molar proportions) similar to the one disclosed U.S. Pat. No. 4,122,110, which is incorporated herein by reference, is utilized to produce an aqueous alcohol stream including mixed lower and higher alcohols. By way of example, in order to prepare the catalyst, 2 liters of an aqueous solution of 483 g of copper nitrate Cu(NO₃)₂, 3 H₂O and 582 g of cobalt nitrate Co(NO₃)₂, 6 H₂O are quickly added to 3 liters of an aqueous solution, heated to 60° C., of 5 moles of sodium carbonate. The resulting precipitate is decanted, carefully washed, dried at 200° C. and then impregnated with an aqueous solution of 18.6 g potassium chromate, so as to introduce 2% of potassium, expressed as K₂O, and then with a solution of 200 g of ammonium dichromate. The product is dried for 2 hours at 200° C., and then heated in air at 450° C. for 2 hours. The resulting powder is made to tablets of 5×5 mm size.

Referring to FIG. 2A, a synthesis gas stream 200 comprising predominantly H₂, CO and CO₂ may be compressed in compressor 201 and then cooled in cooler 202. In an embodiment, the synthesis gas stream 200 fed to compressor 201 may have a feed ratio of H₂/CO/CO₂ of approximately 7/2/1. In an embodiment, the synthesis gas stream 200 is fed to compressor 201 at 100° F., 200 psia, and the gas stream exits the compressor 201 at 337° F., 770 psia. The synthesis gas stream 200 exiting cooler 202 is then combined with a recycled synthesis gas stream 211. The combined stream 212 (140° F., 770 psia, for example) is then compressed at compressor 203. The compressed combined stream 212 exiting compressor 203 (162° F., 870 psia, for example) is then precooled at precooler 204 (to 140° F., 870 psia, for example) prior to entering the reactor 205 which contains the catalyst. In an embodiment, the reactor 205 operates at approximately 870 psia and 608° F.

The effluent stream 213 exiting reactor 205 contains a mixture of alcohols, unreacted synthesis gas, non-volatile gases and water by-product. Compositions of effluent streams exiting reactors in accordance with embodiments of the invention are provide in Table 1 below by dry weight % based upon catalyst compositions.

TABLE 1 Reactor effluent stream composition by catalyst Reactor product composition (dry basis, % weight) *Cr_(0.15)La_(0.15)Al_(0.15)Cu₁Co_(0.5)Na_(0.3) **Cu₁Co₁Cr_(0.8)K_(0.09) Methanol 33.00 19.3 Ethanol 31.03 35.3 i-Propanol 2.96 4.7 n-Propanol 16.02 14.3 n-Butanol 10.5 8.7 other Butanols 2.43 3.1 n-Pentanol 3.98 6.1 other Pentanols 0.7 n-Hexanol 1.9 Total 99.91 97.3 Total C4+ 16.90 20.5 alcohols Weight ratio n- 1.00 to 1.05 1.00 to 1.43 propanol to C4+ *source: reactor product composition for the catalyst described in Example 5 of U.S. Pat. No. 4,346,179 is provided in Table 11 of U.S. Pat. No. 4,346,179 **source: reactor product composition for catalyst B₃ described in U.S. Pat. No. 4,122,110 is provided in Table 1 of Sugier, A., et al.

As indicated in Table 1, about 99.91 weight percent, dry basis, of the effluent stream exiting the reactor is accounted for with a Cr_(0.15)La_(0.15)Al_(0.15)Cu₁Co_(0.5)Na_(0.3) catalyst, which produces about 16.90 by weight C4+ alcohols, dry basis, in the reactor product composition, with a weight ratio of about 1.00 to 1.05 (n-propanol to C4+ alcohols).

As indicated in Table 1, about 97.3 weight percent, dry basis, of the effluent stream exiting the reactor is accounted for with a Cu₁Co₁Cr_(0.8)K_(0.09) catalyst. Assuming the undetermined 2.7 weight percent is not an unmeasured C4+ alcohol, the catalyst produces about 20.5 by weight C4+ alcohols, dry basis, in the reactor product composition, with a weight ratio of about 1.00 to 1.43 (n-propanol to C4+ alcohols), and a weight ratio of about 1.00 to 1.08 (C3 alcohols to C4+ alcohols). It is believed that the undermined 2.7 weight percent may include aliphatic or aromatic C4+ alcohols such as heptanol or other higher alcohols. In such case, this would shift the weight ratio of C3 to C4+ alcohols further in the direction of C4+ alcohols. Assuming the entire undermined 2.7 weight percent is indeed a C4+ alcohol(s), the catalyst produces about 23.2 by weight C4+ alcohols, dry basis, in the reactor product composition, with a weight ratio of about 1.00 to 1.62 (n-propanol to C4+ alcohols), and a weight ratio of about 1.00 to 1.22 (C3 alcohols to C4+ alcohols).

The hot reactor effluent stream 213 (608° F., for example) is then passed through a steam generator/condenser section 206 where stream 213 is cooled and partially condensed on the tube side, and steam is generated on the shell side. As illustrated in FIG. 2A, multiple steam generators/condensers 206A-206D may be utilized in steam generator/condenser section 206. As described in more detail below, steam or hot water produced in steam generators 206A-206D may be provided for use in down-stream reboilers (e.g. as reboiler hot feed water/steam) for energy integration. For example, the steam or hot water produced in steam generators 206A-206D may be provided for use in reboiler 324 to drive distillation column 330 illustrated in FIG. 3, or reboiler 477 to drive distillation column 470 as illustrated in FIG. 4. In an embodiment, the process stream 214 exiting section 206 is reduced to a suitable temperature such as 140° F. at which most of the alcohols and water condense.

The partially condensed process stream 214 is then provided to disengagement vessel 207 where the liquids and non-condensable gases are separated. The non-condensable gases, for example, mainly H₂ and CO with minor concentrations of methane, nitrogen and other components are recycled to compressor 203 as stream 211. Along the way, a small purge stream 215 (e.g. ˜1-2% by volume of stream 211 exiting disengagement vessel 207) is taken to control the build-up of non-condensibles in the recycle loop to 203. In an embodiment, the purge stream 215 is cooled and partially condensed in condenser 208 and provided to knock-out drum 209 to recover any trace amounts of condensed alcohols in the purge stream 215. The condensed alcohols are then recycled to disengagement vessel 207. The purge stream 216 exiting the top of knock-out drum 209 exits the process. In an embodiment, purge stream 216 is utilized as fuel for elsewhere in the process. For example, purge stream 216 may be utilized as fuel to generate steam used to drive process compressors 201, 203.

The aqueous alcohol stream 217 exiting disengagement vessel 207 containing alcohols, water, and small amounts of dissolved gases (mostly CO, some H₂) is then provided to pressure let-down section 220. In an embodiment, multiple stages are used to reduce the pressure of the aqueous alcohol stream 217 to approximately atmospheric pressure. As a result of the pressure reduction, one or more streams 219 containing the previously dissolved gases exit the process. In an embodiment, theses streams can be used for fuel similarly as the purge stream exiting knock-out drum 209. The aqueous alcohol stream 218 exiting pressure let-down section 220 at approximately atmospheric pressure is then provided to the separation train illustrated in FIG. 2B.

Referring to FIG. 2B, the liquid aqueous alcohol stream 218 (1 atm, 113° F., for example) is then fed to the distillation column 230 (operating at 1 atm, 191° F., for example). In an embodiment the energy input into a reboiler (not shown) driving the distillation column 230 is provided by the steam generator/condenser section 206. For example, distillation column 230 may be distillation column 330 in the energy integration scheme illustrated in FIG. 3. In an embodiment, distillation column 230 operates at approximately atmospheric pressure.

The overhead product 231 includes methanol, ethanol, optionally iso-propanol, and a small amount of water associated with the ethanol (and optionally iso-propanol) azeotrope. The bottoms product 232 exiting distillation column 230 contains C3+ alcohols and the balance of the water, and small amounts of the alcohols that were taken overhead (e.g. less than 0.2% by volume of the total volume of the bottoms product). The overhead product 231 may then be provided to distillation column 240 (operating at 1 atm, 173° F., for example). The overhead product 241 is dry methanol, with small trace amounts of ethanol and optionally iso-propanol. The bottoms product 242 includes ethanol, optionally iso-propanol, and substantially all of the water from overhead stream of distillation column 230. In an embodiment, the overhead product 241 exits the process as product methanol. In another embodiment, the overhead product 231 and/or 241, or portions thereof, can be recycled back to reactor 205.

The bottoms product stream 242 may be passed to azeotrope drying unit 260. Therein, the ethanol, and optionally iso-propanol, are separated from water. In an embodiment, an adsorption column can be used to separate the alcohols from water, though other separation technologies could be utilized as known in the art. In an embodiment, the ethanol and iso-propanol, if present, exit the process as a product blend. In an embodiment, the ethanol and iso-propanol are separated and exit the process as separate products.

The aqueous bottoms product stream 232 exiting distillation column 230 may be passed to extraction column 250. Along the way the stream may be cooled in cooler 234. In an embodiment, the stream 232 exits column 230 at approximately 180-200° F. and is cooled to 100° F. at cooler 234. Lower temperatures tend to favor the liquid-liquid equilibrium in the extraction column 250, resulting in less water in the extract. In an embodiment, the extraction column 250 is operated counter-currently where the stream 232 is fed into an upper portion of the column, and a solvent 253 is fed into a lower portion of the column.

In an embodiment, the solvent 253 provided to the extraction column 250 is gasoline where a higher alcohol gasoline blend product is desired. Other solvents may be utilized when an anhydrous alcohol blend product is desired. For example, the extracting solvent 253 provided to the extraction column 250 may be an organic liquid such as decane or a non-polar oxygenate such as an octyl ether, which is largely immiscible with water, has a partition coefficient with respect to butanol and water greater than one, and a vapor pressure low enough to allow the separation of the product alcohols from the solvent via simple distillation. In an embodiment, the extracting solvent 253 additionally has a vapor pressure high enough that the organic liquid can be vaporized in the reboiler of a vacuum distillation column at a temperature less than or equal to 385° F. which facilitates the use of the Fischer-Tropsch reaction exotherm to provide energy to this reboiler.

The extract 251 exiting the top of extraction column 250 contains substantially all of the solvent and at least 99% of the C4+ alcohols and at least 95% of the C3 alcohol(s) provided to column 250, as well as a small amount of water of saturation. In an embodiment, the extract 251 leaves the process as a product. The water of saturation in the extract 251 can optionally be removed in solvent drying section 261 (e.g. by molecular sieve, adsorption column). In an embodiment, the dried extract leaving solvent drying section 261 leaves the process as a product.

The raffinate 252 exiting distillation column 250 contains substantially all of the water fed to column 250 and small amounts of n-propanol (less than 5%) and C4+ alcohols (less than 1%) fed to extraction column 250. In an embodiment, the raffinate 252 is provided to alcohol recovery section 262. In an embodiment, the alcohols are recovered from the aqueous stream through an adsorption process. In another embodiment, the alcohols are recovered from the aqueous stream through a stripper. The alcohol-free water exiting alcohol recovery section 262 may be passed to waste treatment where it exits the process or is used elsewhere in the process. Where a stripper is utilized, the alcohols may be recovered in the form of water-azeotropes and recycled to distillation column 230 or reactor 205. Where an adsorption column is utilized, the alcohols may exit the process as a product blend, or be recycled to 205, 230, 250 or the material exiting 261.

FIG. 3-FIG. 4 illustrate embodiments of thermal integration schemes which may be utilized in coordination with certain features of process illustrated in FIG. 1, catalyst train illustrated in FIG. 2A and separation train illustrated in FIG. 2B. Certain features of the Figures which may be the same or related are identified by similar annotations. For example, the distillation column 330 illustrated in FIG. 3 and the distillation column 430 illustrated in FIG. 4 may be distillation column 230 in FIG. 2B. For example, the extraction column 350 illustrated in FIG. 3 and the extraction column 450 illustrated in FIG. 4 may be extraction column 250 in FIG. 2B. In other instances, similar notation values are provided where appropriate.

FIG. 3 is an illustration of a thermal integration scheme where the alcohols may be extracted into gasoline. Similar to certain features of FIG. 2B, distillation column 230/330 may be utilized to separate the lower alcohols (optionally iso-propanol) and the azeotrope(s) from the higher alcohols, distillation column 240/340 may be utilized to separate methanol from the ethanol-water azeotrope (and optionally iso-propanol), and extraction column 250/350 may be utilized to extract the higher alcohols into gasoline.

In an embodiment, the energy provided from the steam generator/condenser section 206 of FIG. 2A is used to drive distillation columns 330, 340 without the need for additional energy input. For example, distillation column 240/340 used to isolate methanol may be powered without the need for separate energy input. The energy input into reboiler 324 may be effectively utilized twice because the energy from the hot overhead stream 331 exiting the distillation column 230/330 is used to drive distillation column 240/340 through reboiler 326. This also reduces the load on condenser 328. Thus, by effectively using a reboiler for a second distillation column as a condenser (at least partially) for a first distillation column, i.e. a cascade mechanism, one can obtain the separation in the second distillation column at essentially no energy cost. This can be done by adjusting the pressures in the two columns.

An aqueous alcohol feed stream 318 such as stream 218 exiting pressure let-down section 220 in FIG. 2A is passed to economizer 322, where stream 318 is heated against stream 323, the aqueous C3+ bottoms stream from distillation column 330. The heated stream 318 exiting economizer 322 is fed to distillation column 330. For example, economizer 322 can be a shell and tube heat exchanger assembly. The energy input to distillation column 330 is provided by reboiler 324. In an embodiment, energy input to reboiler 324 is provided from the steam generator/condenser section 206 of FIG. 2A. In an embodiment, the energy input to reboiler 324 directly drives the distillation column 330 and indirectly drives the distillation column 340.

The bottoms stream 332 from column 330 is passed to reboiler 324. The reboiler vapor stream 336 from reboiler 324 is returned to column 330. The net bottoms product stream 323 comprising water and C3+ alcohols is passed to economizer 322 where it preheats stream 318 and is subsequently cooled further in cooler 348 and fed to extraction column 350. In an embodiment, extraction column 350 is operated counter-currently where stream 323 is fed into an upper portion of the column, and gasoline 353 is fed into a lower portion of the column. In an embodiment, the extract 351 exiting the top of the column 250 contains substantially all of the gasoline and at least 99% of the C4+ alcohols and at least 95% of the C3 alcohol(s) provided to column 350 and comprises less than 0.2 wt % water. The raffinate 352 exiting distillation column 350 contains substantially all of the water fed to column 350 and small amounts of C3 alcohol(s) (less than 5%) and C4+ alcohols (less than 1%) fed to column 250.

The overhead vapor 331 from distillation column 330 is passed to reboiler 326 where it is partially condensed. The stream 331 exiting reboiler 326 is then fully condensed at condenser 328. A portion of the stream exiting condenser 328 is passed as reflux stream 333 to distillation column 330. The net overhead product stream 335 comprising ethanol and methanol (and optionally iso-propanol), and a small amount of water associated with the ethanol-water azeotrope, is fed to economizer 338 where it is heated against stream 345 and then passed to distillation column 340. The bottoms liquid product stream 342 from column 340 is divided into two streams. Stream 343 is passed to reboiler 326 where it is heated against the condensing overhead vapor stream 331 from distillation column 330. The resulting reboiler vapor stream 343 is exiting reboiler 326 is passed to distillation column 340. Stream 345, which comprises the remainder of stream 342, is sent to economizer 338 where it preheats the stream 335 to column 340 and exits the system as an ethanol-water azeotrope (and optionally iso-propanol) product. If desired, the ethanol-water azeotrope can be dried utilizing techniques known in the art.

The overhead vapor stream 341 from distillation column 340 is passed to condenser 344. Part of the condensed stream is passed as reflux stream 347 to distillation column 340. Stream 349 is the net overhead product from column 340 and comprises substantially dry methanol in the liquid state.

In accordance with some aspects illustrated in FIG. 3, the distillation column 340 may be driven by the reboiler 326 without the need for separate energy input. The energy input into reboiler 324 may be effectively utilized twice because the energy from the hot overhead stream 331 exiting the distillation column 330 is used to drive distillation column 340 in reboiler 326. This also reduces the load on condenser 328. Additional energy integration is found in the economizers 322 and 338. Economizer 322 reduces the load on reboiler 324, and reduces the load on cooler 348. Economizer 338 recovers some of the energy in stream 345 by preheating stream 335 fed into distillation column 340.

FIG. 4 is an illustration of a thermal integration scheme where the alcohols are extracted into a solvent and dry alcohols are subsequently recovered. Similar to certain features of FIG. 2B, distillation column 230/430 may be utilized to separate the lower alcohols (their azeotropes, and optionally iso-propanol) from the higher alcohols, distillation column 240/440 may be utilized to separate methanol from the ethanol-water azeotrope, and extraction column 250/450 may be utilized to extract the higher alcohols into a suitable solvent. Distillation column 470 may be utilized to separate the higher alcohols from the solvent.

In an embodiment, the energy provided from the steam generator/condenser section 206 of FIG. 2A is used to drive distillation columns 230/430, 240/440, 470 without the need for additional energy input. The energy input into reboiler 477 may be effectively utilized three times because the energy from the hot overhead stream 471 exiting the distillation column 470 is used to drive distillation column 230/430 through reboiler 424, and the hot overhead stream 431 exiting the distillation column 230/430 is used to drive distillation column 240/440 through reboiler 426. Thus, by effectively using a reboiler for a second distillation column as a condenser (at least partially) for a first distillation column, and using a reboiler for a third distillation column as a condenser (at least partially) for the second distillation, i.e. a cascade mechanism, one can obtain the separation in the second and third distillation columns at essentially no energy cost. This can be done by adjusting the pressures in the columns.

An aqueous alcohol feed stream 418 such as stream 218 exiting pressure let-down section 220 in FIG. 2A is passed to economizer 422, where stream 418 is heated against stream 423, the aqueous C3+ bottoms stream from distillation column 430. The heated stream 418 exiting economizer 422 is fed to distillation column 430. The energy input to distillation column 430 is provided by reboiler 424. In an embodiment, energy input to reboiler 424 is derived from the overhead vapor stream 471 from distillation column 470 as described further below.

Stream 436 is a portion of the bottoms stream 432 from column 430. Stream 436 is passed to reboiler 424 and heated against stream 471. The heated vapor stream 436 from reboiler 424 is returned to column 430. The net bottoms product stream 423 comprising water and C3+ alcohols is passed to economizer 422 where it preheats stream 418 and is subsequently cooled further in cooler 448 and fed to extraction column 450.

The overhead vapor 431 from distillation column 430 is passed to reboiler 426 where it is partially condensed. The stream 431 exiting reboiler 426 is then fully condensed at condenser 428. A portion of the stream exiting condenser 428 is passed as reflux stream 433 to column 430. The net overhead product stream 435 comprising ethanol and methanol (and optionally iso-propanol), and a small amount of water associated with the azeotropes, is fed to economizer 438 where it is heated against stream 445 and then passed to distillation column 440. The bottoms liquid product stream 442 from column 440 is divided into two streams. Stream 443 is passed to reboiler 426 where it is heated against the condensing overhead vapor stream 431 from distillation column 430. The resulting vapor stream 443 exiting reboiler 426 is passed to distillation column 440. Stream 445, which comprises the remainder of stream 442, is sent to economizer 438 where it preheats stream 435 exits the system as an ethanol-water azeotrope (and optionally iso-propanol) product. If desired, the ethanol-water azeotrope can be dried utilizing techniques known in the art.

The overhead vapor stream 441 from distillation column 440 is passed to condenser 444. Part of the condensed stream is passed as reflux stream 447 to distillation column 440. Stream 449 is the net overhead product from distillation column 440 and comprises substantially dry methanol in the liquid state.

Stream 423 comprising C3+ alcohols and water is passed to the top of extraction column 450. A solvent stream 453 is passed to the bottom of extraction column 450 where it is contacted in counter-current fashion with stream 423. Stream 451 comprises the solvent and substantially all of the alcohol in stream 423. Raffinate stream 452 comprises substantially all of the water and a small amount of C3+ alcohols. Raffinate stream 452 can subsequently be sent to an alcohol recovery system. Stream 451 is passed to economizer 454 where it is heated against stream 453, the net bottoms product of distillation column 470. In an embodiment, the alcohols present in stream 451 are recovered as an overhead product from distillation column 470, and the solvent in stream 451 is recycled to column 450. Optionally, stream 451 prior to passing to economizer 454 can be passed to a drying unit, such as a molecular sieve dryer, to remove trace water.

Stream 472, the bottoms liquid from column 470, is divided into two streams. The net bottoms product stream 453 is passed to economizer 454 where it heats stream 451 and is then passed to cooler 456 and subsequently to extraction column 450. Stream 476, a portion of stream 472, is passed to reboiler 477 where it is heated. The resulting reboiler vapor stream is returned to distillation column 470. In an embodiment, energy input to reboiler 477 is provided from the steam generator/condenser section 206 of FIG. 2A.

The overhead vapor stream 471 from column 470 is passed to reboiler 424 where it is partially condensed against stream 436. Stream 471 is then passed to condenser 473 where it is completely condensed. A portion of the condensate 474 is returned to column 470 as reflux. Condensed stream 475, the net overhead liquid product from 470, comprises dry C3+ alcohols. In an embodiment, the alcohols may then be separated (e.g. by simple distillation) utilizing energy provided from the steam generator/condenser section 206 of FIG. 2A.

In accordance with some aspects illustrated in FIG. 4, the distillation columns 470, 430, 440 may be powered without the need for separate energy input. The energy input into reboiler 477 may be effectively utilized to power each distillation column 470, 430, 440 because the energy from the hot overhead stream 471 exiting the distillation column 470 is used to drive distillation column 430 from reboiler 424, and the hot overheat stream 431 exiting the distillation column 430 is used to drive distillation column 440 from reboiler 426. Thus, the reboilers 424 and 426 provide all the energy needed for the separations in distillation columns 430, 440 by conserving the energy load coming into reboiler 477. Additional energy integration is found in the economizers 454, 422 and 438. Economizer 454 also heats stream 451 entering distillation column 470, thereby reducing the amount of energy which needs to be provided to reboiler 477.

In the foregoing specification, various embodiments of the invention have been described for producing alcohols and gasoline blends with mixed higher alcohols utilizing a low energy separation process. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention as set forth in the appended claims. The specification and drawings are, accordingly, to be regarded in an illustrative sense rather than a restrictive sense. 

What is claimed is:
 1. A method of producing a mixed higher alcohol blend comprising: providing an aqueous alcohol stream including mixed lower and higher alcohols; removing the lower alcohols from the aqueous alcohol stream, resulting in a total weight of C4+ alcohols greater than or equal to a total weight of C3 alcohols in the resultant aqueous alcohol stream; extracting the C3+ higher alcohols from the resultant alcohol stream with a solvent.
 2. The method of claim 1, wherein providing an aqueous alcohol stream comprises passing a synthesis gas comprising hydrogen, carbon monoxide and carbon dioxide through a catalytic zone.
 3. The method of claim 2, further comprising a catalyst comprising Cr, La, Al, Cu, Co and Na.
 4. The method of claim 2, further comprising a catalyst comprising Cu, Co, Cr and K.
 5. The method of claim 1, wherein removing the lower alcohols from the aqueous alcohol stream results in at least a 1:1.4 weight ratio of C3 to C4+ alcohols in the resultant aqueous alcohol stream.
 6. The method of claim 1, wherein removing the lower alcohols from the aqueous alcohol stream comprises providing the aqueous alcohol stream to a distillation column.
 7. The method of claim 6, wherein removing the lower alcohols from the aqueous alcohol stream further comprises removing iso-propanol from the aqueous alcohol stream.
 8. The method of claim 6, further comprising providing an overhead product stream including methanol, ethanol and water associated with the ethanol azeotrope from the distillation column to a second distillation column to separate the methanol.
 9. The method of claim 6, further comprising providing a bottoms product including C3+ alcohols and water from the distillation column to an extraction column.
 10. The method of claim 9, further comprising providing a solvent to the extraction column.
 11. The method of claim 10, wherein the solvent is gasoline.
 12. The method of claim 10, further comprising operating the extraction column counter-currently.
 13. The method of claim 8, wherein energy generated from passing a synthesis gas comprising hydrogen, carbon monoxide and carbon dioxide through a catalytic zone is used to provide energy to a reboiler for driving the distillation column.
 14. The method of claim 13, wherein energy from the overhead product stream from the distillation column is used to provide energy to a second reboiler for driving the second distillation column.
 15. The method of claim 14, wherein no additional energy is required to drive the distillation column, or the second distillation column.
 16. The method of claim 10, further comprising distilling the extract exiting the top of the extraction column in a third distillation column to separate the C3+ higher alcohols from the solvent.
 17. The method of claim 16, wherein energy generated from passing a synthesis gas comprising hydrogen, carbon monoxide and carbon dioxide through a catalytic zone is used to provide energy to a third reboiler for driving the third distillation column.
 18. The method of claim 17, wherein energy from the overhead product stream from the third distillation column is used to provide energy to a reboiler for the distillation column.
 19. The method of claim 18, wherein energy from the overhead product stream from the distillation column is used to provide energy to a second reboiler for a second distillation column.
 20. The method of claim 19, wherein no additional energy is required to drive the distillation column, the second distillation column, and the third distillation column. 